1. Field of the Invention
The present invention relates to improvements in optical lens systems providing a real image. In particular, the present invention relates to improvements in providing an optical lens design utilizing duplicate lens component parts for the low cost production of cameras.
2. Description of the Prior Art
Photographic objectives are presently known in the field of low cost cameras. For example, the Altman U.S. Pat. No. 3,194,116 and the Melech U.S. Pat. No. 3,438,697 disclose photographic objectives of the simple triplet type. This lens system has the advantage of providing relatively good correction for aberrations and is frequently referred to as the Cooke triplet. The Altman patent in particular discloses the value from a cost view point of utilizing lens elements made entirely of injection molded plastics. Both of these patents are dependent upon an inner negative biconcave lens element having a relatively thin thickness along the optical axis to permit achromatizing of the entire lens system.
Plastic lens systems utilizing more than three elements are also known in the prior art such as the Willoughby et al U.S. Pat. No. 3,749,477. This reference simply discloses an anamorphic lens system having four lenses made from the same plastic and adapted to be attached as a supplement to a fixed lens camera.
Finally, a glass projection lens system having a 1:1 magnification is disclosed in the McCrobie U.S. Pat. No. 3,817,599. The McCrobie lens system is designed to provide a multi-focal projection lens wherein the basic lens group has a symmetrical conjugate relationship. Basically, the prior art has experienced some limited success in providing low cost cameras with plastic lens. However, manufacturing problems have existed for instance in the injection molding of thin biconcave negative lenses.